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In an earlier publication 1 we reported aspects of magnetokinetic studies on the oxidation of FeS2 carried out as a function of its particle size (90 to 250μm) and temperature (400–500 °C); in this study we considered mostly the formation of α and γ Fe2O3. In the present paper we have considered the formation of other oxidation products such as (a) Fe2  (SO4)3, and (b) superparamagnetic particles of α Fe2O3. Mössbauer spectroscopy has confirmed the presence of (a) and, coupled with X-ray line broadening studies has shown the absence of (b). The yield of Fe2  (SO4), is found to increase with decreasing starting particle size of FeS2. Using our earlier results 1 we have obtained values of (dM/dt) from the initial slopes of the magnetization (M) vs. time curves for particle sizes (180 to 250 μm). From plots of ln (dM/dt) versus 1/T an activation energy of ∼7 Kcal/mole has been obtained for the following predominant reaction: FeS+(11/4)O2→ (1/2) αFe2O3+2SO2. This value compares favorably with values reported by other workers2 who used classical thermogravimetric analysis.

The variation of the periodicity along the C axis (N'C) as a function of temperature in Fe9S~0 where W' varies between 5 and 1 over the range 300 -600 K, has been investigated.The antiferromagnetic to ferrimangetic (A) phase transition is explained in terms of a vacancy rearrangement.Using absolute-reaction-rate theory and measurements of magnetization as a function of time at constant temperature around the A. transition, coefficients of diffusion for iron atoms along the C axis have been determined over the range 440 to 484 K and found to be -10 8 cm /sec. Appropriate mechanisms for the diffusion process are also considered.

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Soft x-ray emission spectra are obtained of sulfur in FeS, Fe0.9S, Fe0.875S, and Fe0.5S. The structure in the Kβ emission spectra is consistent with recent SCF-Xα calculations for ferrous iron in an octahedral crystal field. Broadening in the Kβ emission spectra with decrease in the Fe-S bond distance is in agreement with the trends predicted by the SCF-Xα calculations. The charge on the sulfur ions is calculated from the shifts of the Kα emission lines. Calculated charges on FeS and Fe0.5S are in good agreement with previous LCAO calculations and photoemission data. Shifts in the Kα line positions for Fe0.9S and Fe0.875S indicate that electroneutrality is satisfied by a reduction in charge on sulfur rather than the coexistence of ferrous and ferric iron. The Auger spectra of sulfur show sharp structure for FeS which gradually disappears as the sulfides become more cation deficient. The Auger data is discussed in terms of changes in the electronic density of states in the valence band as predicted by the SCF-Xα calculations.